Three types of nonlinearity in physics of radiation force and acoustical streaming.

Abstract

Thousands of papers on radiation force (RF) and acoustical streaming (AS) have been published since Faraday, Rayleigh, and Langevin. There have been more papers on RF in biomedicine published in the last decade than were written in the entire 20th century. Nevertheless, some nonlinear acoustic phenomena significant for engineering and biomedical applications are still misunderstood. The presentation contains discussions regarding frequently occurring inaccuracies and contradictions. In particular, it features three types of nonlinearities which can appear independently. First, equations for RF, which are nonlinear by themselves, can contain the nonlinear modulus of a medium. Second, the nonlinear distortion of the acoustic field, depending on sound intensity and geometric and physical nonlinearities, can govern the RF and AS. Third, hydrodynamic nonlinearity often appears at the development stage of streaming. The latter nonlinearity may be observed in weak acoustic fields if RF acts for a long period of time on a low‐viscosity fluid. Evaluations and formulas are given, indicating conditions for separate observation of each type of nonlinearity. Some contradictions existing in the literature are resolved. Experimental data illustrating developed theory are shown.